Whole‐ecosystem oxygenation experiments reveal substantially greater hypolimnetic methane concentrations in reservoirs during anoxia

Hounshell, Alexandria G.; McClure, Ryan P.; Lofton, Mary E.; Carey, Cayelan C.

doi:10.1002/lol2.10173

Cited by 27 publications

(23 citation statements)

References 32 publications

(77 reference statements)

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“…The presence of vegetation may also be beneficial for reducing GHG emission, as seen in previous studies 44 and is responsible for increasing C burial rates 22 . Finally, aeration systems are commonly used to prevent anoxia and could therefore reduce CH 4 emissions, as shown in experimental studies on hypolimnetic DO manipulations 45 .…”

Section: Resultsmentioning

confidence: 99%

Florida’s urban stormwater ponds are net sources of carbon to the atmosphere despite increased carbon burial over time

Goeckner

Lusk

Reisinger

et al. 2022

Commun Earth Environ

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Stormwater ponds are engineered ecosystems designed for flood control and sediment retention in urban watersheds. They are the most commonly used stormwater control measure in the USA, but their biogeochemical processes and impacts are often overlooked. Here, we assessed the potential impact of stormwater ponds on regional carbon cycling by coupling carbon burial rates and fluxes of carbon dioxide and methane gases in five sites over an age gradient of 14–34 years. Carbon burial increased logarithmically with site age, ranging from 22 to 217 g carbon m−2 y−1, while, median floating chamber diffusive gas fluxes were 1290 g carbon dioxide m−2 y−1 and 5 g methane m−2 y−1, which, when combined as carbon dioxide equivalents, equates to 2900 g carbon dioxide eq m−2 y−1. Comparing carbon burial to gas flux reveals that stormwater ponds can be net carbon sources and need to be considered for regional and global carbon models.

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Section: Resultsmentioning

confidence: 99%

Florida’s urban stormwater ponds are net sources of carbon to the atmosphere despite increased carbon burial over time

Goeckner

Lusk

Reisinger

et al. 2022

Commun Earth Environ

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“…Thus, we hypothesized that when aerators are placed in such a system, the physical movement of all that water, with the fact that methane has low solubility, would enhance an atmospheric methane flux. To our knowledge, there is only one other study in a temperate lake that has studied oxygen effects on methane dynamics, and they found a remarkable decrease in methane build-up with engineered aeration (Hounshell et al, 2021), yet they did not quantify air-water flux. With our dataset, we were able to directly calculate this flux when the aerators were ON versus OFF to determine the impact of aeration in terms of methane dynamics.…”

Section: Discussionmentioning

confidence: 98%

“…Engineered aeration efforts work by either destratifying the water column or directly injecting oxygen to the water (Harris et al, 2015;Stigebrandt et al, 2015;Koweek et al, 2020). This has also been commonly done in small lake systems (e.g., Martinez and Anderson, 2013;Hounshell et al, 2021) and reservoirs (McCord et al, 2016). While aeration should relieve the low oxygen problem to create habitat for metazoan life, prevent the noxious release of sulfide from sediments, and enhance coupled nitrification-denitrification, an additional potential consequence is that aeration could also enhance atmospheric methane emissions in estuaries.…”

Section: Introductionmentioning

confidence: 99%

The Effects of Engineered Aeration on Atmospheric Methane Flux From a Chesapeake Bay Tidal Tributary

Lapham

Hobbs

Testa

et al. 2022

Front. Environ. Sci.

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Engineered aeration is one solution for increasing oxygen concentrations in highly eutrophic estuaries that undergo seasonal hypoxia. Although there are various designs for engineered aeration, all approaches involve either destratification of the water column or direct injection of oxygen or air through fine bubble diffusion. To date, the effect of either approach on estuarine methane dynamics remains unknown. Here we tested the hypotheses that 1) bubble aeration will strip the water of methane and enhance the air-water methane flux to the atmosphere and 2) the addition of oxygen to the water column will enhance aerobic methane oxidation in the water column and potentially offset the air-water methane flux. These hypotheses were tested in Rock Creek, Maryland, a shallow-water sub-estuary to the Chesapeake Bay, using controlled, ecosystem-scale deoxygenation experiments where the water column and sediments were sampled in mid-summer, when aerators were ON, and then 1, 3, 7, and 13 days after the aerators were turned OFF. Experiments were performed under two system designs, large bubble and fine bubble approaches, using the same observational approach that combined discrete water sampling, long term water samplers (OsmoSamplers) and sediment porewater profiles. Regardless of aeration status, methane concentrations reached as high as 1,500 nmol L−1 in the water column during the experiments and remained near 1,000 nmol L−1 through the summer and into the fall. Since these concentrations are above atmospheric equilibrium of 3 nmol L−1, these data establish the sub-estuary as a source of methane to the atmosphere, with a maximum atmospheric flux as high as 1,500 µmol m−2 d−1, which is comparable to fluxes estimated for other estuaries. Air-water methane fluxes were higher when the aerators were ON, over short time frames, supporting the hypothesis that aeration enhanced the atmospheric methane flux. The fine-bubble approach showed lower air-water methane fluxes compared to the larger bubble, destratification system. We found that the primary source of the methane was the sediments, however, in situ methane production or an upstream methane source could not be ruled out. Overall, our measurements of methane concentrations were consistently high in all times and locations, supporting consistent methane flux to the atmosphere.

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“…On a seasonal basis, thermal stratification can lead to the depletion of oxygen, nitrate, and other terminal electron acceptors in the BBL and hypolimnion (Eckert and Conrad 2007; Deemer and Harrison 2019). The resulting anoxia facilitates CH 4 flux into the hypolimnion (Hounshell et al 2021), and seasonal shifts in CH 4 and electron acceptor concentrations may stimulate rapid responses in methanotrophy in the water column (Saarela et al 2020; Mayr et al 2020 a , b ). On an hourly to daily basis, many lakes experience a basin‐wide internal wave (or seiche) that drives fluctuations in BBL conditions (Wüest and Lorke 2003).…”

Section: Figmentioning

confidence: 99%

In situ flux estimates reveal large variations in methane flux across the bottom boundary layer of a eutrophic lake

D’Ambrosio

Henderson

Nielson

et al. 2022

Limnology & Oceanography

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Methane (CH4) produced in anoxic sediments plays a significant role in the carbon economy of many lakes and reservoirs. CH4 released from sediments first crosses the bottom boundary layer (BBL), the layer of water overlying the lakebed where currents are slowed by friction with the sediments below. Physical and biogeochemical conditions in the BBL, which can fluctuate hourly to daily with basin‐wide internal waves (seiches), likely influence CH4 transport from sediments into the hypolimnion. In this study, we estimated CH4 fluxes across the BBL of a eutrophic lake using a novel in situ flux gradient approach adapted from marine applications. For 2–6 h periods throughout the spring and summer, we estimated CH4 fluxes across the BBL using simultaneous measurements of CH4 concentrations, turbulent mixing, and thermal stratification. Sub‐daily variation in CH4 fluxes was high, and CH4 fluxes sometimes changed several‐fold within hours. These rapid shifts in BBL fluxes were likely influenced by fluctuations in seiche‐driven variations in the intensity of BBL turbulent mixing. Fluxes increased from spring to summer, concurrent with the development of lake stratification, and fueled an accumulation of CH4 below the thermocline. Throughout the summer, CH4 flux across the BBL exceeded CH4 accumulation below the thermocline, suggesting significant methanotrophy in the hypolimnion, consistent with incubation‐based oxidation rates. Our results are the first to demonstrate sub‐daily and seasonal variability in the timing and magnitude of CH4 fluxes within a lake BBL, and highlight a need to quantify such variability in other lentic systems.

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Whole‐ecosystem oxygenation experiments reveal substantially greater hypolimnetic methane concentrations in reservoirs during anoxia

Cited by 27 publications

References 32 publications

Florida’s urban stormwater ponds are net sources of carbon to the atmosphere despite increased carbon burial over time

Florida’s urban stormwater ponds are net sources of carbon to the atmosphere despite increased carbon burial over time

The Effects of Engineered Aeration on Atmospheric Methane Flux From a Chesapeake Bay Tidal Tributary

In situ flux estimates reveal large variations in methane flux across the bottom boundary layer of a eutrophic lake

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